Back in the lab,
looking today at casts of early Homo erectus crania. Homo erectus first emerges in
the fossil record around 1.75, 1.8 million years ago. As a species, it encompasses a
broad range of fossil evidence and in fact, the
latest specimens that we call Homo
erectus are less than a half million years old. We are going to look
specifically at the earliest evidence
of Homo erectus in this lab between around 1.8
million years ago and around 1.4 million
years ago. During this time frame from 1.8
to around 1.4 million years ago, Homo erectus occurred in Africa
and broadly across Africa. We have casts here
representing Kenya and Tanzania, but it also occurred in
Ethiopia and in South Africa. And Homo erectus occurred in
Asia with very early occurrence of Homo erectus possibly as
early as 1.8 million years ago on the island of Java and a
good sample of Homo erectus from around 1.75
million years ago from the Republic of Georgia. So, we are looking for the
first time in hominin evolution at a species that spread beyond
the boundaries of the continent of Africa and migrated to
other parts of the world where it established successful
occupations of those areas. There's something really
different about Homo erectus. Now, when we look at a skull of
Homo erectus, and this is one of the most well-known
skulls, this is KNM-ER 3733, it's from Ileret on the
east side of Lake Turkana and it has many of the classic
features of Homo erectus crania from throughout the world. Compared to a human skull,
it is relatively long in the brain case
and relatively low. You can that this skull
was sort of elongated. If we put it next
to a human skull, you'll see that the human skull
is much higher and much rounder than the Homo erectus skull. This is a characteristic
that's shared by every Homo erectus
skull in the fossil record. However, when we look at
the faces of these crania, you can see that the face of
this Homo erectus skull is around the same size
as a human face. It's related to the brain case
in a similar way to humans. It has a nose, if you
look very carefully at it, a nose that projects
forward away from the face and cheekbones that are more
gracile than the cheekbones of most australopithecines. What's different about
this skull compared to a human skull aside from its
overall shape is the occurrence of this very clear
supraorbital torus, a structure that we
call the brow ridge. You can see the supraorbital
torus here is a ridge that extends forward
away from the orbits and that continues right out to
the outside corners of the eyes. This is a really distinctive
structure in Homo erectus. It's similar to the
supraorbital torus that occurs in chimpanzee
skulls. You can see that they also
have a distinct bar of bone that extends over both orbits, but this is not something
that's shared by ancestry with chimpanzees. If we look at other
kinds of early hominins, for example this
skull of Homo habilus, we see a much less pronounced
supraorbital development. If we look at other
kinds of early hominins, for example this skull of
Australopithecus africanus, again, we see a much less
pronounced brow ridge than in this example
of early Homo erectus. And the brow ridge in
particular, we are looking here at a skull of Homo erectus
that has one of the thinnest, least pronounced brow ridges. We can look at this skull
which is from Olduvai Gorge around 1.4 million years ago and you'll see the very thick
brow ridge, a brow ridge that was nearly a centimeter
thick all the way across. What's going on with
that feature? This is really distinctive
and it's something that modern humans
really rarely have. What we do see in modern
human sometimes a development of the brow ridge especially
centrally and occasionally in some human populations
today, we have a brow ridge on the outside of
the orbits too. It's not entirely clear
what the evolutionary cause of this brow ridge in
early Homo erectus was. It is something that continues on throughout the Pleistocene
hominin fossil record. We are going to see it in
other kinds of early hominins. If I had to lay out
my favorite hypothesis for what the brow
ridge is doing, it's there to protect the eyes. You have a thick bar
of bone over your eyes and that protects them and
buffers them from injuries that might come from
in front or from above. We do find on early skulls of Homo erectus evidence
of cranial wounds. For example, this skull
from Dmanisi in the Republic of Georgia, it's got a
depression right here on top of it that appears
to be a healed wound that was a suffered a blow to the head sometime during
this individual's life. We don't know that that's the
only reason for brow ridges. Many anthropologists think
that they may also have a role in resisting stress that
comes from heavy chewing, but we know that it's
really distinctive, that these early
specimens of Homo erectus, they have this brow ridge,
they have an increasing degree of buttressing in other
parts of the skull, including a thickened temporal
line and an angular torus, here a thickening here on the
back of the skull associated with the back of the temporalis
muscles, a nuchal torus which extends at very
top of the neck muscles and their attachment on the back
of the skull, a thickened bar of -bone that attaches there. And as we move forward in time
in the Homo erectus record, these skulls get thicker
and thicker in terms of the actual bone thickness. Homo erectus looks like they
were built for butting heads and if that is evidence of
some sort of conflict or use of weapons, it would
be very interesting. But when we look at Homo
erectus generally in comparison with earlier hominins, the brow
ridge is an outlier in terms of looking less human than
other features of the skeleton. When we look at the body size
of Homo erectus, we are looking at individuals that were
human-like in their body size and I want to be really clear
when I mean by human-like because this is a source
of confusion when we think about the variation
of early Homo. Every australopithecine
that we know of was relatively
small in body size. Now obviously encompasses
a range of variation, but it's a range of variation
that's very much like the range of variation of living
chimpanzees. The largest australopiths
probably overlapped in body size with the smallest living humans, but the overlap was
not real great. When we look at human
populations around the world today, we
see a big range of body sizes. For example, I'm around
6 feet 2 inches tall or that's just a little
under 190 centimeters tall. My wife is about is
5 feet 3 inches tall, she's about 160 centimeters
tall. That's a normal range
of variation here in the United States, especially
considering men and women. In some other populations, we have radically
smaller body sizes. It's normal in some populations
to be 145 centimeters tall or around 4 foot 7 or 8. So, that range of body sizes, which encompasses some living
human hunter-gatherer groups going up to the largest
body size living humans; that's pretty extensive and
we can say clearly that, the australopithecines,
they were smaller. Homo erectus varied a lot. This is a humerus of
Homo erectus from Kenya, it's also from the east
side of Lake Turkana and as you can see it's
broken off at the top, but it's around the
size of my humerus, maybe even a little bigger. We have other long
bones that indicate that there were large
individuals, as large as it's common to
be in modern day America, Western Europe, East Asia. So, we have a range
of body sizes that includes a large form. At Dmanisi in the Republic of
Georgia, we have got post crania that represent a very
nice skeletal sample with four really
complete crania. The post cranial
bones indicate a range of body sizes that's smaller than what we know
about in East Africa. A juvenile individual, here's
his skull, around 10 years old, stood around 145
centimeters tall. A larger individual was
around 160 centimeters, around 5 foot 3 inches tall,
which is a typical size for males in some living
human hunter-gatherer groups, such as those in
Southern Africa. So, when we look at Homo
erectus, we are not looking at a species that was
uniformly tall or large in a human context, we're
looking at a species that was human sized where
humans today are a range of body size in different
populations around the world. It's interesting to consider
the variation among the crania and mandibles of these early
Homo erectus individuals because when we look in
the context of East Africa, we have skulls like this one
which has a brain size that's over 800 cubic centimeters
and we have very small crania with brain sizes around
600 cubic centimeters. Looking at the Republic
of Georgia in the sample from Dmanisi, we have
crania like this one, which have small brains,
around 600 cubic centimeters, and at least one skull which
has an even smaller brain, around 550 cubic
centimeters, another skull with a larger one, around 750. So, there's variation. This variation is larger
than the brain sizes of any earlier hominins, larger
than the average brain size in Homo habilis, but nevertheless
overlapping with Homo habilis. Compared to humans
who have a brain size around 1400 cubic centimeters,
these earliest examples of Homo erectus are a little
less than half our size. Looking at the mandibles,
we get a lot of information about what the teeth
and diet might have been like of these early Homo erectus
individuals, and one thing that you'll notice right away is that unlike robust
australopithecines who have hugely expanded
post canine teeth, these teeth are a
lot like human teeth. They are human-like in size,
more or less, and human-like in the relation of the premolar
teeth to the molar teeth. They are also human-like
in the size and form of the anterior teeth,
but I will say that that's not without
variation. For example this
mandible from Dmanisi, represents the largest
skull, the largest individual that we know of at the site
and has teeth that rival in size the teeth of
robust Australopithecines. Here we've got a jaw of
Australopithecus boisei and you can see that although
boisei has clearly bigger teeth, and the teeth of this early
Homo erectus individual are proportioned like human
teeth, in particular with human-like incisors
and canines relative to their premolars and
molars, nevertheless, these are both really
large, really robust jaws. So, Homo erectus encompassed
a variation that went to relatively powerful
chewing even though they appear to have had a more human like
diet than other early hominins. So, what's the big idea
about Homo erectus? If we look at Homo erectus
as a group, we are looking at the emergence of the
human-like body size and that comes along
with a human-like and possibly a little more than human-like pattern
of variability. Their diet had shifted to
a more human-like diet, which means that they are
generalized, they are relying on a range of food resources, that range of food resources
based on stable isotope data and microwear data
from the teeth looks like it included meat. Certainly, that confirms what
we are seeing from stone tools, from evidence of butchering
animals breaking into bones, they are using higher energy
food resources including meat and they are living a different
lifestyle from earlier hominins. That different lifestyle
has consequences in the shape of their bodies. Their bodies are
more human-like. They are living as
hunter-gatherers today do and that lifestyle has a range
of body size in different parts of the world that work with it. So, the big idea is that Homo
erectus is basically human-like under the neck. Above the neck, we can see
that there is a lot of anatomy that is very specialized
in these early parts of Homo erectus and we'll expect to see a different evolutionary
pathway when we look forward in time into later hominins.
